Specific Gravity of Gemstones — Reference Table

Common SG lookups: Diamond 3.50–3.53  ·  Ruby 3.97–4.05  ·  Sapphire 3.95–4.03  ·  Emerald 2.67–2.78  ·  Quartz 2.63–2.65  ·  Tourmaline 3.01–3.26  ·  Almandine Garnet 3.93–4.30  ·  Zircon 4.60–4.80  ·  Cubic Zirconia 5.60–6.00  ·  Turquoise 2.60–2.90

Specific gravity (SG) is the ratio of a gemstone's mass to the mass of an equal volume of water. It is a dimensionless measure of density and one of the most reliable constants for gemstone identification. Unlike RI, SG can be measured on rough stones and irregular fragments with no polished surface — though not on mounted stones, since hydrostatic weighing needs a loose stone. That makes it particularly valuable for rough material where a refractometer reading is impossible.

In the field, gemologists determine SG using hydrostatic weighing — the stone is weighed in air and then in water, and the ratio gives the SG. Electronic scales with a suspension bridge attachment make this fast and accurate. Heavy liquids (such as methylene iodide at 3.32 or bromoform at 2.89) provide a quick floating/sinking test without arithmetic. For most stones, RI + SG together narrow the candidate list to one species.

High-SG stones include cassiterite 6.80–7.10, zircon 4.60–4.80, and spessartine garnet 4.12–4.18. Low-SG materials include amber 1.05–1.09, jet 1.10–1.40, and ivory 1.70–1.98. The wide overlap between similar-looking stones (e.g., various garnets, or green tourmaline vs. tsavorite) is resolved by a precise hydrostatic SG measurement combined with RI.

Measuring SG yourself? The number you can trust out of a hydrostatic weighing depends on your balance and on how big the stone is — a 0.01 ct scale resolves a five-carat stone to about ±0.03 and a half-carat one only to ±0.32. How to measure specific gravity covers the two bench setups, which formula goes with each, and what any given scale can actually decide. Already have the two weights? The specific gravity calculator does the arithmetic and shows which species the result does not rule out.

All instrument charts: Refractive Index  ·  Mohs Hardness  ·  Birefringence  ·  Fluorescence  ·  Pleochroism  ·  Spectroscope  ·  Optic Character  ·  Chelsea & Hanneman Filters  ·  Dispersion  ·  Magnetism

See also: Full Reference Database  ·  Exam Study Guides  ·  Open dataset (CSV & JSON, CC BY 4.0)

What is the specific gravity of diamond?
Diamond's specific gravity is 3.50–3.53. Simulants read differently — cubic zirconia is far denser at 5.60–6.00, which is why a hydrostatic SG measurement separates them quickly.

Which gemstone has the highest specific gravity?
Among the 132 gems in this reference, Cinnabar is the densest at 8.00–8.20. The full table below ranks every species from highest to lowest.

How is specific gravity measured?
By hydrostatic weighing: weigh the stone in air, then suspended in water — the ratio gives SG. It works on rough and irregular loose stones with no polished surface, but not on mounted stones, where the setting's metal makes the measurement meaningless. Loupewise publishes a step-by-step guide to measuring specific gravity.